Distribution strip for absorbent products

ABSTRACT

An absorbent structure which includes a fluid storage layer comprising matrix fibers (e.g., cellulose fluff fibers) and superabsorbent polymers positioned above a distribution strip. The strip comprises cellulosic fibers (e.g., cotton linters, mercerized cellulose, fluff pulp, or chemically treated cellulose) having a basis weight of between 45 g/m 2  and 140 g/m 2 , preferably between 75 g/m 2  and 110 g/m 2 , and a density of between 0.20 g/cc and 0.60 g/cc, preferably between 0.25 g/cc and 0.55 g/cc. The absorbent structure may also comprise a fluid pervious top sheet and a fluid impervious back sheet. The structure may be used in diapers, feminine hygiene pads or adult incontinence pads.

This application claims the benefit of Ser. No. 60/139,163 filed Jun.14, 1999.

FIELD OF THE INVENTION

The present invention relates to an absorbent structure includingchemically treated and mercerized cellulose fibers for improved liquiddistribution for use in disposable absorbent structures such as infantdiapers, feminine hygiene pads and adult incontinence pads.

BACKGROUND OF THE INVENTION

Absorbent products, such as infant diapers, feminine hygiene pads, adultincontinence pads, and the like, have traditionally utilized structureswith various configurations and materials to provide the requisiteabsorbency performance. One objective in developing improved absorbentproducts has been to increase both the total absorbent capacity of theproduct, as well as the tenacity and reliability with which suchproducts absorb and retain fluid loads. Another objective has been toprovide thinner and more comfortable absorbent products.

To manage liquid body waste, the absorbent structure or structureswithin an absorbent product must generally be able to first uptake aliquid into the absorbent product, then distribute the liquid within theabsorbent product, and finally retain the liquid within the absorbentproduct.

One way for improving the absorbency characteristics of an absorbentproduct has been to use entangled masses of fibers, e.g., non-wovenfibrous webs, which can imbibe and retain liquids, such as dischargedbody fluids and other body exudates, both by absorption (e.g., fluid istaken up by the fiber material itself and retained in the capillaryinterstices between the fiber) and by wicking (e.g., fluid isdistributed through diffusion and stored in the capillary intersticesbetween fibers). Typically, however, structures of this type have had alimited storage capacity for fluids, a low rate of distributing fluids,and a limited ability to partition fluids from other materials.

Conventional fluff cellulose fibers and superabsorbent polymers arewidely used for the absorbent core of absorbent products. Superabsorbentpolymers (hereinafter “SAPs”) are capable of absorbing many times theirown weight of liquid. SAPs have been used to increase the absorbency ofabsorbent products such as infant diapers, feminine hygiene pads andadult incontinence pads.

While an absorbent core of fiber and SAPs can provide improved storagecharacteristics, they can have shortcomings in transporting ordistributing absorbed body fluids laterally from one region or zone toanother. This can be troublesome in some products where body fluids arefrequently discharged in periodic discrete gushes, and each gush offluid discharged in this manner will generally encounter an absorbentstructure with diminished capabilities to quickly and efficiently: (1)acquire subsequent gushes of fluid, (2) move fluid from the commondischarge area to other unused, unsaturated, or relatively dry parts ofthe absorbent structure, (3) remain resistant to compression deflection,(4) recover from wet compression, and (5) partition fluids. Thus, thetotal absorbent capacity of the absorbent product is often not fullyutilized.

It is an object of the present invention to provide an absorbent articleable to exceed the wicking, partitioning or distribution characteristicsof known absorbent structures.

Furthermore, it is an object of the present invention to have anabsorbent structure that is capable of quickly distributing the liquidthroughout the absorbent product.

SUMMARY OF THE INVENTION

The present invention is directed to an absorbent structure for use in adisposable absorbent product for absorbing bodily fluids. The absorbentstructure includes a fluid storage layer including matrix fibers and asuperabsorbent polymer for receiving fluids and a distribution strippositioned below said fluid storage layer. The distribution stripincluding cellulosic fibers and has a basis weight of between 45 gramsper square meter and 140 grams per square meter and has a density ofbetween 0.20 grams per cubic centimeter and 0.60 grams per cubiccentimeter.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an exploded, perspective view of the components of anabsorbent product with the distribution strip of the present invention.

FIG. 2 is a perspective view of a horizontal wicking test apparatusemployed in the Examples of the present specification.

FIG. 3 is a perspective view of a rate of advance test apparatusemployed in the Examples of the present specification.

FIG. 4 is a graph illustrating the results of a horizontal wicking testperformed on absorbent structures of the present invention.

FIG. 5 is a graph illustrating the result of a rate of advance testperformed on absorbent structures of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The present invention concerns a distribution strip useful for laterallywicking fluid. The distribution strip is particularly suitable as acomponent of a disposable absorbent product, such as a diaper. In such aproduct the distribution strip is ideally positioned beneath anabsorbent storage component of the absorbent product.

The distribution strip is provided as a fibrous web. As used herein, theterm “fiber” or “fibrous” is meant to refer to a particular materialwherein the length to diameter ratio of such particulate material isgreater than about 10. Conversely, a “nonfiber” or “nonfibrous” materialis meant to refer to a particulate material wherein the length todiameter ratio of such particulate material is about 10 or less.

The fibers used in manufacturing the distribution strip may bechemically treated or mercerized. Preferred fibers include cellulosicfluff pulp, mercerized cellulose pulp, cotton linters and cellulosefluff pulp treated with polyvalent metal ions (e.g., aluminum, calciumor magnesium). Mixtures of these fibers may also be employed.

The distribution strip may be manufactured from individual fibers byeither wetlaid or airlaid processes, although wetlaid processing ispreferred. Additives typically used in wetlaid processes, such as wetstrength resins (e.g., polyamide epichlorohydrin) may also be included.

Alternatively, the distribution strip may be made by an airlaid process,either as a separate web, or laid down as an integral layer with theother layers of the structure.

The basis weight of the distribution strip is preferably between 45grams per square meter (gsm) and 140 gsm, and most preferably between 75gsm and 110 gsm. The density of the distribution strip is preferablybetween 0.20 grams per cubic centimeter (g/cc) and 0.60 g/cc and mostpreferably between 0.25 g/cc and 0.55 g/cc.

In use, the distribution strip may be positioned in an absorbentstructure in any orientation for which lateral (or X-Y) wicking ofabsorbed fluid is desired. For example, the absorbent structure in aconventional disposable diaper, as shown for example in FIG. 1, includesin order, a fluid permeable topsheet, a fluid acquisition anddistribution layer (ADL), a tissue, a fluid storage layer or core(typically including SAP particles), a distribution strip (also known asa wicking strip), and a fluid impermeable bottom sheet (a backsheet). Afluid insult introduced to the diaper (in the Z-direction) penetratesthe topsheet and is readily absorbed by the acquisition and distributionlayer. The fluid is then distributed by the ADL which is designed toallow the liquid to wick laterally (in the X-Y direction). Finally fluidmigrates from the ADL into the storage layer where it is absorbed by thefiber matrix and SAP particles.

Although a conventional diaper design as described above generally workswell, one disadvantage is that in use, absorbed fluid tends to pool inone lateral region of the diaper (generally the front of the diaper). Itwould be desirable to provide a diaper which more efficiently wicksfluid from one portion of the diaper (e.g., the front) to another (e.g.,the back) portion of the diaper which is generally underutilized.

The distribution strip of the present invention may be positionedbetween the fluid storage layer and the fluid-impermeable backsheet. Inuse, excess fluid collecting between the storage layer and the backsheetsheet migrates into the distribution strip. The fluid then migrateslaterally along the distribution strip to another region of the storagelayer which has not exceeded its storage capacity. The fluid thendiffuses into the storage layer. In this way, the storage capacity ofthe diaper is more efficiently utilized.

The distribution strip of the present invention may be employed in anyabsorbent product where lateral wicking of fluid is desired. In additionto diapers, the distribution strip may be used in feminine hygieneproducts, and adult incontinence products.

EXAMPLE 1

A distribution strip according to the present invention was made as awetlaid handsheet. Cellulose fluff pulp (Foley fluff pulp, BuckeyeTechnologies Inc., Memphis, Tenn.) was disintegrated in a TAPPIdisintegrator (British Pulp Evaluation Apparatus, Mavis Engineering,Ltd., London, England). The fluff pulp was disintegrated for 600 counts(˜5 minutes). While the raw material is disintegrating, the DynamicHandsheet Former (Formette Dynamique, Centre Technique de L'industriedes Papiers Cartons & Celluloses) was readied for use.

A fine meshed forming screen is placed in the centrifuge basket of thehandsheet former and smoothly molded to the sides of the basket. Thespray arm is positioned within the centrifuge basket, being careful toensure that the spray head does not come in contact with the bottom ofthe basket, and locked in place. The fiber slurry reservoir is filledwith approximately 14 liters of water. The centrifuge basket isactivated and brought up to speed, then water is added until the waterfully covers the forming screen. At this point, the slurried fiber istaken from the disintegrator and added to the slurry reservoir, and thepaddle agitator is activated in the reservoir.

The delivery system is readied by setting the flow valve and activatingboth the spray arm and the pump. The spray arm continues to cycle at1200 rpm until the slurry reservoir has been emptied. Water is slowlydrained from the centrifuge basket by opening the drain valve. An effortis made to prevent the centrifuge RPM's from dropping more than 10%during this process. Once all the water has been removed, the centrifugeis turned off and the brake is applied. When the basket stops, the sprayarm is removed, and the formed sheet is split at the seam where theforming screen overlaps. The sheet and the screen are removed from thecentrifuge basket and transferred to a single drum steam dryer with a40″ circumference. The formed sheet was 36″ in length. Repetitive passesthrough the dryer may be required to bring the sheet to a fully driedcondition. Sheets were made at a basis weight of 77.5 gsm and 108.5 gsm.Once dried, the sheet was densified by compression to a target densityof 0.3 g/cc.

EXAMPLE 2

The experiment of Example 1 was repeated except that mercerizedcellulose pulp (HPZ grade, obtained from Buckeye Technologies Inc.,Memphis Tenn.) was substituted for the fluff pulp.

EXAMPLE 3

The experiment of Example 1 was repeated except that the cellulose pulpwas previously treated with approximately 7000 ppm of AlSO₄,precipitated according to papermaking techniques.

EXAMPLE 4

The experiment of Example 1 was repeated except that cotton linter pulp(Grade 702, obtained from Buckeye Technologies Inc., Memphis Tenn.) wassubstituted for the fluff pulp.

Horizontal Wicking Test

The handsheets of Example 1-4 were subjected to horizontal wickingtests. A Kamas Cell Mill (Kamas Industri AB, Sweden) disintegrated Foleyfluff pulp sheets to produce fluff for the absorbent core. A pad former(Buckeye Technologies Inc., Memphis, Tenn.) was used to combine SAP,SXM9100 (Stockhausen) and fluff in a 30% to 70% ratio in order toprepare 14″×14″ absorbent core test pads. Test pads were constructed ata basis weight of 0.30 g/in² and compressed to a density of 0.15 g/cc. Adistribution strip was cut to 4″×14″ and conditioned in a controlledhumidity and temperature room before testing. The distribution stripswere constructed at a basis weight of 77.5 g/m² and compressed to adensity of 0.30 g/cc. The samples were then placed onto a level platformwith bordering grooves to capture “runoff” fluid (0.9% saline). (SeeFIG. 2 for wicking apparatus.) An acquisition-distribution layer (ADL)from a commercial diaper cut to 3″×7″ was placed on top of the samplewhere fluid was introduced. A second board was placed on top of thesample and ADL. The top board contained an insult reservoir with a 1 ½″inside diameter. The insult region, relative to the sample, was 5″centered from the front end or end closest to insult reservoir. Two4,539 g weights placed on the top board along with the weight of the topboard supplied about 0.40 lbs/in² of pressure perpendicular to thesample. Three 100-ml insults were introduced to the sample attwenty-minute intervals. After one hour, the sample was then sectionedand weighed to determine the distance that liquid was transported awayfrom the insult region. Horizontal wicking was quantified by the sum ofthe last three inches of wicking in the absorbent core on a gram offluid per gram of SAP/fluff sample basis. Absorption capacity forSAP/fluff and ADL was recorded. Table 1 details the effect ofincorporating the wicking strip into an absorbent product.

TABLE 1 Wicking Components of Absorbent Core and Last three inches inthe Distribution Strip absorbent core (g/g) Core—50% SAP & 50% Fluffcellulose 11 Core—70% SAP & 30% Fluff cellulose 15 Core—70% SAP & 30%Fluff cellulose 22 Distribution Strip—100% Fluff cellulose Core—70% SAP& 30% Fluff cellulose 26 Distribution Strip—100% Mercerized celluloseCore—70% SAP & 30% Fluff cellulose 22 Distribution Strip—Chemicallytreated cellulose Core—70% SAP & 30% Fluff Cellulose 23 DistributionStrip—Cotton linters

Rate of Advance Test

Distribution strips were cut to 4″×14″ and conditioned as above beforetesting. The distribution strips were constructed at a basis weight of77.5 g/m² and compressed to a density of0.30 g/cc. The samples were thenplaced onto a level platform with a Teflon coated mesh. A photograph ofthe testing apparatus is shown in FIG. 3. Attached to the platform was afluid head box with ¼″ tubing connected to a vertically adjustable fluidreservoir. The front edge of the distribution strip sample was centeredabove the head box. The head box was designed with four {fraction(3/16)}″ diameter holes that were spaced {fraction (9/16)}″ apart. Thefluid (0.9% saline) level was adjusted to maintain zero head pressure.Once the sample touched the head box, fluid distributed along thesample. When the fluid reached the end of the sample the fluid reservoirwas adjusted to prevent further fluid flow. Fluid distributed by thesample was measured as fluid rate in grams per second. Sample absorbencyand fluid flow rate were recorded.

TABLE 2 Fluid Rate Absorbency Distribution Strip Fiber g/sec g/g 100%Fluff cellulose 0.11 7.5 100% Mercerized cellulose 0.08 8.6 100%Chemically treated cellulose 0.05 5.8 100% Cotton linters 0.12 7.6

What is claimed is:
 1. An absorbent structure for use in a disposableabsorbent product for absorbing bodily fluids, said structurecomprising: a fluid storage layer including matrix fibers and asuperabsorbent polymer for receiving fluids and a distribution strippositioned below said fluid storage layer, said distribution stripincluding cellulosic fibers selected from the group consisting of cottonlinters, mercerized cellulose, chemically treated cellulose and mixturesthereof, wherein the chemically treated cellulose is treated with apolyvalent ion selected from the group consisting of aluminum, calcium,magnesium and mixtures thereof, and said distribution strip having abasis weight of between 45 grams per square meter and 140 grams persquare meter and having a density of between 0.25 grams per cubiccentimeter and 0.55 grams per cubic centimeter, wherein one hour afterthree 100 ml insults to the structure at 20 minute intervals in alast-three-inches-of-the-fluid-storage-layer-longitudinal-and-transverse-horizontal-wickingtest, the fluid storage layer has horizontal wicking of 22 g/g orgreater.
 2. The absorbent structure of claim 1 wherein said absorbentproduct is selected from the group consisting of diapers, femininehygiene pads and adult incontinence products.
 3. The absorbent structureof claim 1 wherein said distribution strip has a basis weight of between75 grams per square meter and 1 10 grams per square meter.
 4. Theabsorbent structure of claim 1 wherein said distribution strip is madeby a wet-laid process.
 5. The absorbent structure of claim 1 whereinsaid distribution strip is made by an air-laid process.
 6. An absorbentproduct for acquisition, distribution and storage of bodily fluids, saidproduct comprising: a fluid pervious top sheet; a fluid imperviousbacksheet; an absorbent structure disposed between said topsheet andsaid backsheet, said absorbent structure including: a fluid acquisitionand distribution layer; a fluid storage layer positioned beneath theacquisition and distribution layer and in fluid communication therewith,said storage layer including SAP, wherein one hour after three 100 mlinsults to the structure at 20 minute intervals in alast-three-inches-of-the-fluid-storage-layer-longitudinal-and-transverse-horizontal-wickingtest, the fluid storage layer has horizontal wicking of 22 g/g orgreater; and a distribution strip positioned beneath the fluid storagelayer and in fluid communication therewith, said distribution stripincluding cellulosic fibers selected from the group consisting of cottonlinters, mercerized cellulose, chemically treated cellulose and mixturesthereof, wherein the chemically treated cellulose is treated with apolyvalent ion selected from the group consisting of aluminum, calcium,magnesium and mixtures thereof and said distribution strip having abasis weight of between 45 grams per square meter and 140 grams persquare meter and having a density of between 0.25 grams per cubiccentimeter and 0.55 grams per cubic centimeter.